Ring-opening polymerization is a polymerization process in which polymerization proceeds as a result of ring opening of a cyclic compound as a monomer to synthetically yield a polymer. Industrially important synthetic polymers such as nylons (polyamides), polyesters, polyethers, polyethyleneimines, and polysiloxanes are now produced through ring-opening polymerization.
In general, a catalyst must be added to a reaction system so as to develop ring-opening polymerization. The catalyst herein acts upon the cyclic compound and accelerates its ring-opening reaction. For example, catalysts for cation-reactive monomers such as cyclic ethers, cyclic formals, and cyclic imines include Lewis acids such as BF3.O(C2H5)2, SnCl4, and AlCl3; alkyl halides such as alkyl chlorides and alkyl bromides; super strong acids such as CF3SO3H; esters of super strong acids, such as CF3SO3R, wherein R represents an alkyl group; and cation salts such as R3C+PF6− and R3O+BF4−, wherein R represents an alkyl group. Catalysts for anion-reactive monomers such as cyclic siloxanes, lactams, and acid anhydrides include Li, Na, K, RCOONa, RONa, and R2NLi, wherein R represents an alkyl group. As a catalyst for a fluorooxetane, there is disclosed an alkali metal fluoride supported on a support such as an activated carbon. In this catalyst, however, the active site is the alkali metal fluoride, and the activated carbon only plays a role as a support (Patent Document 1). Catalysts for coordinate anion-reactive monomers such as cyclic ethers and lactones include, for example, (C2H5)2Zn—H2O, (C2H5)2Zn—ROH, and AlR3-acetylacetone-H2O, wherein R represents an alkyl group; and those for metathesis reactive monomers such as cyclic olefins include MoCl5 and WCl6.
However, when these known catalysts are used, 1) side reactions other than polymerization may occur, and/or 2) residual catalysts, if remained in the resulting polymers, may exhibit some toxicity or may cause deterioration in performance of the polymers.
In contrast, activated carbons have been known to be used as adsorbents and supports for solid catalysts but have not yet been known to be usable, if used alone, as catalysts for ring-opening polymerization.
Patent Document 1: Japanese Examined Patent Application Publication No. 1-49340 (Claim 5)